In EP 326 198 (published in 1989) cooking or salad oils are disclosed that comprise triglycerides that contain 60-92 wt % oleic acid; 5-25 wt % linoleic acid; 0-15 wt % linolenic acid, while less than 3 wt % saturated fatty acids are present.
According to the above EP document the oils can be prepared along a completely chemical route (as exemplified in example 1), by a solid liquid adsorption process, using a specific adsorbent and a specific solvent system (as exemplified in example 2) or by a chromatographic method (as exemplified by example 3). However, none of the above methods of preparation is economically feasible and therefore the above methods are unattractive.
From FR 2 685 706 a process is known for the preparation of pharmaceutical compositions with a diglyceride support. The diglycerides can be made by glycerolysis of liquid oils. However the products obtained are still high in saturated fatty acids (about 9-10 wt %), while the methodology applied for the glycerolysis is not well disclosed.
According to WO 90/12858 long chain fatty acid triglycerides, including poly unsaturated long chain triglycerides can be prepared by lipase-catalyzed interesterification of long chain free acids or lower alkyl esters thereof with short chain triglycerides. The triglycerides should have low contents of mono- and diglycerides. The liberated short chain free fatty acids are removed by evaporation during the enzymic conversion.
Therefore this document does not reveal a process for the preparation of low SAFA-oils, wherein relatively large amounts of diglycerides are present. Neither does this document disclose a process wherein the SAFA-content of the end product is controlled by the solubility of the different conversion-products formed during the reaction.
According to U.S. Pat. No. 5,225,580 highly unsaturated triglycerides are obtained by subjecting an interesterification reaction product to sequential chromatographic separation. However the products that are low in SAFA, which are obtained by this process, are also low in diglycerides (col. 4, 1. 54-62), while these triglycerides also contain high levels of C.sub.18:1 (c.f.: table 12: raffinate).
According to WO 91/08676 (published in 1991) trans-esterified low saturated liquid oils can be prepared. Those oils contain less than 3.5 wt % saturated C.sub.12 -C.sub.18 fatty acid and at least 96% unsaturated C.sub.12 -C.sub.22 fatty acids, while the weight ratio mono-unsaturated (=MUFA) to poly-unsaturated fatty acids (=PUFA) ranges from 10 to 0.5. The above-mentioned oils further comprise 2-15 wt % of diglycerides and 85-98 wt % of triglycerides.
The above-mentioned oils are obtained from an unsaturated fatty acid source material (C.sub.12 -C.sub.22 unsaturated fatty acids and/or its esters) and a vegetable oil, high in MUFA and/or PUFA by performing an enzymic interesterification. After removal of free fatty acids and/or its esters, the product oil is collected.
Therefore, the above-mentioned method requires the use of starting materials that are very rich in mono- and/or poly-unsaturated fatty acid materials. Moreover, the diglyceride content of the end product is maximized to 15 wt %.
Another disadvantage of the above-mentioned prior art is that the product liquid oils are limited in its PUFA-content (in particular the C.sub.18:2 content). Recently Roberts c.s. disclosed in Br. Heart Journ. (1993), 70, p. 524-529 that there is an inverse relation between the risk of sudden cardiac death and the linoleic acid content in the adipose tissue. So, in effect it should be expected that the healthiest liquid oils should not only be low in SAFA, but also relatively high in PUFA, in particular rich in C.sub.18:2.
The prior art, however, does not reveal a commercially attractive process for the preparation of those oils.